Several existing devices are used for facilitating spontaneous breathing in anaesthetised patients; traditionally, the Endotracheal Tube (ETT) and more recently the Laryngeal Mask Airway (LMA). The majority of these devices use an inflatable cuff(s) to create the anatomical seal and as a consequence there is an incidence of co-morbidity associated with their use; both physiological and anatomical. Subsequent refinement of the LMA has resulted in the development and introduction of supraglottic airway devices (SAD) with gastric drainage (GD). The reported advantages being ease of insertion, haemodynamic stability, decreased morbidity, improved respiratory mechanics and reduced incidence of pulmonary aspiration. An alternative development uses a pre-formed and non-inflatable cuff. Disadvantages of SAD with GD primarily relate to the configuration of the distal tip becoming bulbous by the presence of the gastric tube passing through the inflatable cuff and the associated structures employed; to present a flat profile of the distal tip when the inflatable cuff is deflated immediately prior to deployment and; prevent occlusion of the drain tube after the SAD is deployed and inflated in situ.
The visco-elastic characteristics of the materials used for construction of the various SAD's exert significant influence over the ability of the device to deliver the above stated advantages and contribute significantly to the disadvantages. SAD's use the same materials as existing LMA devices. Semi rigid PVC, vinyl elastomers and liquid silicone rubbers are predominant in combinations comprising a more rigid airway with a softer inflatable cuff whilst thermoplastic elastomers (TPE) are used for versions exhibiting a non-inflatable cuff. Those devices using PVC and LSR require the use of adhesives and solvents for bonding and joining the different components during manufacture. SAD's using TPE do not require adhesives as they are essentially a one piece more rigid airway tube covered with TPE material to form the required shape without an inflatable cuff.